Abstract:

Article Preview

Silicon carbide (SiC) has become the substrate of choice for III-N epilayers applied to
electronic devices due to the lack of a native III-N substrate. This is particularly true for high
power applications, since the thermal conductivity of the substrate enhances device performance.
Although the GaN lattice match is slightly better for SiC than for sapphire, the dislocation densities
that result are still very high (generally in the high 108 cm-2 range) and often deleterious to device
performance. Screw-component dislocations are especially critical since they serve as leakage
paths in vertically conducting III-N devices.
In this paper efforts to reduce the extended defect density in III-N films grown on SiC will be
reviewed. Details on recent efforts to use step-free SiC mesa surfaces arrayed on commercial 4HSiC
substrates will then be highlighted showing dramatic reductions in extended defect densities
and the virtual elimination of critical defects for vertically conducting devices. In these
experiments, SiC surfaces that are homoepitaxially grown step-free or of very low step density have
been used as growth templates for thin (<3 μm) GaN films deposited on a novel 1000 Å AlN
nucleation layer characterized by a total dislocation density two orders of magnitude lower than the
previous state-of-the-art, and with no evidence of screw-component dislocations.

Abstract: The influence of surface preparation of 4H-SiC substrates on structural properties of GaN grown by low pressure metalorganic vapour phase epitaxy was studied. Substrate etching has an impact on the crystallographic structure of epilayers and improves its crystal quality. The GaN layers were characterized by RBS/channelling and HRXRD measurements. It was observed that on-axis 4H-SiC is most suitable for GaN epitaxy and that substrate etching improves the crystal quality of epilayer.

Abstract: A high-quality crack-free AlN cap layer on GaN layer has been achieved using an AlN buffer layer directly grown on a silicon substrate at high temperature by radio frequency (RF) plasma-assisted molecular beam epitaxy. A two dimensional (2D) growth process guide to AlN cap layer of high grade crystal quality. The nucleation and the growth dynamics have been studied by in situ reflection high energy electron diffraction (RHEED) and ex situ by high resolution transmission electron microscopy (HR-TEM). The microstructure was investigated by energy-dispersive X-ray spectroscopy (EDX). It was disclosed that AlN is single crystalline with low defect. High densities of V-shaped pits were not detected at the interface between AlN and GaN layers. Contradictory the earlier reported V-shaped defects in nitride-based alloys; these V-shaped pits were condensed on top of the AlN layer because of H2 etching of the surface when a high temperature growth discontinuity between AlN and GaN layers.

Abstract: In this paper, InGaN/GaN/AlN/Si (111) structure was grown using a plasma-assisted molecular beam epitaxy (PA-MBE) technique. The structural and optical properties of grown film have been characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), high resolution X-ray diffraction (HR-XRD) and photoluminescence (PL). Indium-mole fraction has been computed to be 0.27 using XRD data and Vegards law with high grain size and low tensile strain. Room-temperature photoluminescence revealed an intense peak at 534 nm (2.3 eV) related to our sample In0.27Ga0.73N.

Abstract: AlN single crystals were prevented from cracking by simultaneous growth and evaporation of SiC substrates. The freestanding crystals (<1 mm thick) were proved continuous by synchrotron phase contrast imaging and used as a model system to investigate the type of dislocation structure near AlN/SiC interface by x-ray diffraction techniques. We have found that, unlike the situation in GaN films, where predominantly edge-type threading dislocations cross the layer along its normal, the dislocations configure to form mosaic structure. We suggest a theoretical model that describes the misfit stress relaxation in growing AlN crystal.